Stretching nylon filaments in a gas vortex



1970 E. H. SUNDBECK STRETCHING NYLON FILAMENTS IN A GAS VORTEX Filed May13, 1965 4 3 0 w rIll/IIIIZMIIIII INVENTOR- EDWARD H. SUNB CK ATTORNEYUnited States Patent 3,551,549 STRETCHING NYLON FILAMENTS IN A GASVORTEX Edward H. Sundbeck, Chapel Hill, N .C., assignor to MonsantoCompany, St. Louis, Mo., a corporation of Delaware Filed May 13, 1965,Ser. No. 455,394 Int. Cl. B294: 17/02; F26b 3/04 US. Cl. 264-490 3Claims ABSTRACT OF THE DISCLOSURE Thermoplastic filaments and especiallynylon filaments are highly stretched by a process of rapidly heating thefilaments by subjecting the filaments to a high temperature gas vortexand simultaneously stretching the filaments whereby high tenacityfilaments are obtained. The draw ratio can be 5.5:1 and above, and thegas temperature can be from 250 C. to 325 C.

This invention relates to the drawing of filamentary strands. Moreparticularly, the invention is directed to an improved process andapparatus for drawing yarns, particularly of tire cord count, at highdraw ratios.

Normally, in the production of continuous filament yarns, the as-spunfilaments are drawn or attenuated. The purpose of this drawing is toimpart a molecular orientation along the filament axis to therebyincrease the tensile strength or tenacity of the filament. The greaterthe attenuation, or the higher the draw ratio obtained during this drawprocess, the greater the tensile strength attained in the filaments.Ofttimes the drawing is conducted at room temperature, commonly termedcold-drawing. In the case of tire cords, however, in which relativelyhigh tensile strengths are necessary and which, therefore, requiregreater draw ratios, the filaments must be drawn at elevatedtemperatures in order to attain the necessary degree of attenuationwithout undue filament breakage.

One method by which tire cords are attenuated and oriented by thisso-called hot drawing procedure, is by employing a hot slot arrangement.In this method, the yarn is advanced by a set of godet rolls to andaround a draw pin, where the yarn is drawn and then forwarded by the useof a second set of godet rolls,

commonly referred to as draw rolls. The hot slot is employed between thedraw pin and the draw rolls to heat the yarn to permit the attainment ofhigh draw ratios and consequent high tensile strengths. This hot slot,as commonly employed, usually consists of a milled slot formed in aseries of aluminum blocks held together in laminated fashion to form acomposite block which averages 4 feet in length, as measured along thepath of the yarn being processed. Though dimensions are found to varysomewhat, a typical size would be one-half inch deep by three-sixteenthsinch in width. In other words, the slot is of such dimensions that itwill allow passage of the yarn through the heated blocks with a minimumclearance to promote rapid heat transfer, yet providing sufficientclearance to keep the yarn from coming in contact with the walls of theslot. Each longitudinal zone of a foot or so in length of the compositeblock is heated by electrical resistance heaters which may be thermistorcontrolled so that the temperature block can be maintained at anydesired temperature between 200 and 300 C. The yarn passing through theslot is heated mainly by convection from the hot air surrounding theyarn bundle, although a small amount of heat is transferred to the yarnby radiation from the surface of the heated metal block.

In this hot slot method of drawing tire cords, there are severaldisadvantages and undesirable features. One of the most undesirablefeatures is that the rate of heat transfer from the hot slot to the yarnis very low. This is due, at least in part, to the fact that the yarntravels through what is essentially stagnant hot air within the slot.Because of this, a bulky long piece of equipment must be employed, oftengreater than 4 feet in length, in order to allow for sufficient heattransfer to the yarn to obtain the temperatures necessary to conducthigh draw ratio operations. Additionally, because of the openconfiguration of the hot slot, it is not economically feasible to employa gas other than air as a heat transfer medium even though other gaseshave a higher coefficient of heat transfer. It would be desirable, inthe drawing operation, to employ a non-oxidizing medium, such asnitrogen, in order to prevent degradation and yellowing of the yarnsduring exposure to the high temperatures incident to conventional hotslot processing. Another disadvantage of the hot slot is that thetemperature of the hot stagnant air within the slot cannot beascertained with any great accuracy and, because of the design of theequipment, the variation in temperature along the length of the slot maybe subject to considerable variation, rendering it very ditficult todetermine the optimum operating conditions for a given production run.

With the above in mind, it therefore becomes an object of the presentinvention to provide a process and apparatus for obtaining yarn ofultra-high tensile strength.

Another object of the present invention is to provide an improvedprocess and apparatus for drawing tire cord to very high draw ratios.

A further object of the subject invention is to provide a process andapparatus for increasing the rate of heat transfer from a hot gas to ayarn moving at high speeds.

Still another object of this invention is to provide an improved processand apparatus whereby nylon yarns may be drawn at precisely controllabletemperature levels to thereby promote product uniformity.

These and other objects and advantages of the present invention willbecome apparent from the following detailed description thereof, whenconsidered in connection with the accompanying drawings, wherein likereference numerals designate like or similar parts and in which:

FIG. 1 is a diagrammatic perspective view illustrating one embodiment ofan apparatus designed to carry out the process of this invention;

FIG. 2 is an elevational view, partly in section, illustrating oneembodiment of the heat transfer apparatus used in carrying out theprocess of this invention, and

FIG. 3 is a cross-sectional view of the apparatus shown in FIG. 2 takenalong line 3-3 of FIG. 2 and showing details of construction of the heattransfer device.

-In general, according to the invention, there is provided an improvedprocess and apparatus for drawing continuous filament yarns at highspeeds and high draw ratios, which apparatus is designed for eflicientand economical operation. This efliciency and economy is made possibleby the use of a novel heat transfer device wherein the runningcontinuous filament yarn may be heated to very high temperatures over asmall linear distance. The stated objectives are attained by feedingyarn from a suitable source of supply through a feed roll assembly afterhaving been passed through or around a suitable tensioning device, ifdesired. At least one roll of the feed roll assembly is positivelydriven. As is well known, the purpose of the feed roll assembly is toprovide a supply of yarn at a predetermined and precisely controllablerate with the provision that the yarn will undergo slippage through thefeeding assembly due to the attenuating tensions subsequently to beapplied. Upon leaving this first roll assembly, the yarn passes over andaround a stretch or draw pin and the attenuation of the filaments tendsto be localized at this draw pin. In the portion of the yarn pathdownstream of the first roll assembly and drawing pin, there is disposeda heat transfer device, the details of which constitute an importantaspect of this invention. While passing through such a heat transferdevice, the traveling yarn is heated to very high temperatures over ashort linear distance. This rapid heating to high temperatures isaccomplished by the use of hot gases entering the heat transfer devicetangential to the path of the yarn, to thereby flow around and alongwith the yarn in a centrifugal or cyclonic fashion through theapparatus. Once the yarn leaves the heat transfer device, it passesthrough and around a draw roll assembly of a construction similar tothat of the previously mentioned feed roll assembly. At least one of therolls of this draw roll assembly is positively driven in order that theyarn may be stretched or attenuated between the feed and draw assembliesat a predetermined draw ratio to thereby impart the desired amount ofdraw or attenuation to the yarn between the two roll assemblies. Afterbeing drawn, the yarn is forwarded through a guide and is taken up inpackage form by any suitable means, such as a traversing ring travelerarrangement.

Referring now to FIG. 1 of the drawings, wherein the apparatuscomprising one aspect of this invention is shown in a typicalarrangement, a thermoplastic, draw-orientable yarn, indicated generallyby reference numeral 10, in the form of a tow or bundle of substantiallyparallel, undrawn filaments, is supplied from a yarn source. The yarnsource can be, for example, in the form of a yarn package 12 previouslydolfed from a conventional spinning machine. While the invention will bedescribed primarily in connection with an apparatus which employs a yarnpackage so doffed, it is to be borne in mind that this is merely for thepurpose of convenient illustration and is in no sense to be taken as alimitation since the apparatus, according to the present invention, mayas well be employed in the processing of continuous yarns which have notbeen previously doffed from a filament spinning machine.

As shown, yarn is passed over and around one end of bobbin 14, or othersuitable yarn holder, such as a pirn or cone. The yarn 10 is threadedaround any suitable tensioning device 16 which functions to maintain anorderly and uniform supply of yarn. From the tensioning device 16, theyarn 10 is, if convenient, passed through a yarn guide 18, thence to arotatably arranged thread advancing means in the form of a pair ofcontiguous feed rolls 20 to thereby withdraw the yarn from bobbin 14 andsupply same at a controlled rate. The rolls are mounted on parallel axesand engage each other in operation to effectively nip the yarn passingtherethrough so that slippage or free-flight of the yarn between therolls is prevented.

From thread advancing means 20, the yarn 10 is passed about draw pin 22where the attenuation is largely localized. The pin is mounted axiallyaskew with respect to the parallel axes of the feed rolls and have asmooth, wear resistant yarn contact surface. After being passed aboutpin 22 a desired number of turns, the yarn is passed through heattransfer device 24, which is seen to consist of upper and lowercommunicating portions or chambers, 26 and 28, respectively, as bestviewed in FIG. 2. This heat transfer device has a yarn inlet opening 30and a yarn outlet opening 32 and is so constructed that its lowerportion 28 takes the form of an inverted, truncated cone. The hot gasesemployed to heat the yarn enter the heat transfer device through gasinlet 34; a small portion of these gases leave the apparatus through gasoutlet 36. A major portion of the hot gases will normally escape throughyarn inlet 30 located at the upstream end of the heat transfer deviceand thus preheat the yarn to some extent before it enters the apparatus.

After passing through the heat transfer device 24, the

yarn 10, emerging through lower yarn outlet 32, is passed about a pairof rotatably arranged draw rolls 38 which are arranged to be operated ata predetermined increase in speed relative to the feed roll arrangement20 to thereby attain the desired draw ratio. After leaving the drawrolls 38, the yarn is fed vertically downward to be taken up, usuallythrough a pigtail-type yarn guide 40, in an orderly manner by a suitableform of package building apparatus. As shown in FIG. 1, the yarn 10 istaken up by a ring-traveler assembly, generally denoted by referencenumeral 42, which is seen to comprise a bobbin 44 adapted to be rotatedby a driven belt 46 to collect a package of yarn 48. The assemblyfurther comprises a vertically reciprocable traveler ring 50 carrying aring-traveler 52 adapted to revolve freely about bobbin 44 as the yarnis twisted a desired amount and wound about the bobbin.

Reference is now made to FIG. 2, wherein the heat transfer device 24comprising one aspect of this invention is shown on a large, partiallysectionalized scale for greater clarity. This heat transfer apparatusconsists of an upper chamber 26 and a lower chamber 28 communicatingtherewith. A yarn inlet opening 30 is formed in the upper end of upperchamber 26 and an outlet opening 32 is formed at the lower end of lowerchamber 28. Additionally, a hot gas inlet 34 and gas outlet 36 areprovided by which there is circulated a suitable heating medium throughthe heat transfer tube 24. The upper chamber 26 generally takes the formof a hollow cylinder, while that of the lower portion 28 is of thegeneral form of an inverted truncated cone. The purpose of the conicallower portion 28 is to aid in creating a centrifugal vortex orcyclonic-like flow to the hot gases employed as the heat transfermedium. Such a shape additionally aids in directing the hot gas flowthrough the body of the heat transfer device and out through gas outlet36. Yarn inlet 30 at the upstream end of the apparatus can assume avariety of shapes and dimensions, preferably being somewhat larger thanthe yarn bundle to be processed to thereby provide an additional exitfor the hot gases in addition to the gas exit 36, whereby the filamentsentering the apparatus will be preheated in their travel from thesnubbing or draw pin 22 to the heat transfer device. Yarn outlet 32leading from the apparatus should be sufficiently small in diameter toavoid excessive loss of hot gases from the device, but sufficientlylarge enough to freely; permit passage of the yarn bundle. Hot gas inlet34 should be near the top of the upper chamber 26 of the heat transferdevice and should be sufiiciently large in size to permit hot gas attemperatures in the range of 250-325" C. to pass therethrough at ratesof 50-100 feet per second (f.p.s.). Gas outlet or eliminator 36 shouldbe located near the base of the lower conical section of the apparatus.When the apparatus is in operation, gas inlet 34 may be connected to anysuitable source of hot gas supply, not shown. Also, both the hot gasinlet and the gas outlet may be connected to a closed system which mayprovide for the supply, recycling and reheating of a hot gas. If sodesired, a gas eliminator or outlet 36 may, of course, be vented to theatmosphere. Additionally, when a noncondensible gas or vapor is used inthe treatment of the yarn, outlet 36 need not be employed and may evenbe blocked off. However, if a condensible vapor, such as steam, is used,this outlet 36 can be employed to effect removal of the condensedmedium.

Most relatively inert gases which can be heated to high temperatureswithout decomposing are suitable for use in the process of thisinvention, some examples being air, nitrogen, helium, steam, and evenhydrogen if proper safety precautions are taken. The heat transferdevice is additionally provided with a small, spherical reservoir ortrap 37 which has been found useful when vaporous heating mediums, suchas steam, are employed. By applying a small vacuum to outlet 36, whichis arranged to communicate with the lower regions of the reservoir,condensate accumulating therein is easily removed, along with minoruncondensed portions of the heating medium.

Reference is now made to FIG. 3 as showing a crosssection of the heattransfer device taken along line 3--3 of FIG. 2. As seen, the heattransfer apparatus is essentially circular in cross-section, having twoconcentric circular openings in the form of an inlet opening 30 and anoutlet opening 32. Hot gas inlet 34 is mounted to be off-center withrespect to the vertical axis of the heat transfer device and can be seenas nearly tangential to the inside circumference of chamber 26. Thepurpose of offsetting the hot gas inlet is to create a vortex flow ofhot gases around the yarn passing therethrough. This form of gas flow,which combines transverse, rotary and longitudinal components, greatlyincreases the rate of heat transfer to the yarn. Because of this greatlyincreased heat transfer, yarn may be processed at increased rates withgreater product uniformity.

In carrying out the typical examples which follow, the heat transferdevice was constructed of glass. Its construction is, however, notlimited to glass, but may be made of many other suitable materials, suchas the metals.

As before related, it has been discovered that filamentary yarns of athermoplastic, fiber-forming polymer which have not beenstretch-oriented can be treated according to this invention to imparthigher draw ratios to thereby obtain increased tensile strengths. Theyarn is continuously passed through a stretching zone wherein thefilaments are rapidly heated to an elevated temperature by the use ofhot gases circulating within the heat transfer device in a centrifugalor cyclonic fashion, whereby heat transfer to the filaments is greatlyincreased to thereby permit higher draw ratios, resulting in highertensile strengths. The process of the invention, because of the greatlyincreased rate of heat transfer to the yarn, also provides a muchshorter processing distance for hot drawing operations.

The method of the present invention is applicable to a wide variety ofcontinuous filament yarns, the only requirement being that the yarn ismade from a thermoplastic, fiber-forming resin which can be extended bydrawing to show an increased molecular orientation along the filamentaxis. The yarns may be formed by known techniques from these resins,including melt extrusion and wet spinning and dry spinning processes. Asexamples of fiber-forming synthetic polymers formed from thermoplasticfiber-forming resins which may benefit from the present invention, theremay be mentioned polyethylene, polypropylene, polyurethanes,polycarbonates, etc. The process of this invention is applicableparticularly to the treatment of nylon yarns, including nylon 66, nylon4, nylon 6, nylon 610, nylon 1, and fiber-forming copolymers thereof.

This invention may be further illustrated by reference to the followingexamples, although it will be understood that these examples areincluded for purposes of illustration only and are not intended to limitthe scope of the invention.

EXAMPLES I-V For the purpose of drawing yarns according to the processand by means of the apparatus of this invention, a heat transfer devicesimilar to that shown in FIG. 2 was employed. The yarn treating zonedefined by the heat transfer device was approximately 4 inches inlength, 1 inch in diameter at its widest point and approximately ir inchin diameter at its narrowest section, i.e., at a point immediatelyupstream of outlet tube 36. The yarn inlet opening 30 was approximately/2 inch in diameter and extended down into the yarn treating sectionapproximately 1 inches, while the hot gas inlet was approximately inchin diameter. The yarn exit and gas outlet were both approximately 2 mm.in diameter. In the above description all diameters are to be taken asinside diameters.

The filaments to be processed were prepared from the melt spinning ofpolyhexamethylene adipamide. The yarn obtained was composed of 140undrawn filaments, each having a denier of approximately six. The yarnwas fed through the system depicted in FIG. 1 of the drawing and intothe heat transfer device 24 at an input speed of 31.4 feet per minute(f.p.m.). Nitrogen gas was used in these examples as the heat transfermedium and was fed through the hot gas inlet at a rate of 1 cubic footper minute (measured at room temperature) and exhausted through the gaseliminator and outlet tube to the atmosphere. Yarns exhibiting thefollowing tabulated properties of draw ratio, tenacity and elongationwere obtained when employing nitrogen gas at the temperatures indicated:

Temperature Tenacity, Elongation, Example of N2 gas, 0. Draw ratiog.p.d. percent EXAMPLE VI In this example, nylon yarn identical to thatused in the first five examples was drawn by use of the previouslydescribed hot slot in lieu of using the heat transfer device of thisinvention. The hot slot was approximately 4 feet in length and thesurface temperature of the aluminum block was maintained at 260 C. Themaximum draw ratio obtainable using this device was 5.5 which gave ayarn tenacity of approximately 10.5 grams perdenier (g.p.d.), which isseen to be lower than that of either Examples I-V.

EXAMPLE VII In this example, nylon yarn identical to that used in theprevious examples was drawn on a drawtwister under optimum conditions inlieu of using the heat transfer device of this invention. Employing thebest possible settings in the two-stage position of the drawtwister, theyarn could be drawn to a maximum draw ratio of 5.56. This draw ratioproduced yarn having a tenacity of approximately 10.6 g.p.d., againresulting in a lower tenacity than that obtainable by the centrifugalheat transfer device of this invention.

In accordance with another embodiment of the present invention, theconical section 28 of heat transfer device 24, as shown in FIG. 2, maybe filled, or partially so, with small glass beads ranging in size from3 to 6 mm. The addition of such beads was found to increase the rate ofheat transfer within the device to the traveling yarn. When using thismodified system, the yarn contacted the hot glass beads to produce arolling action to thereby promote better heat transfer contact with thethreadline. Because of the increased heat transfer from the hot glassbeads to the running bundle of filaments, maximum draw ratios andmaximum tensile strength could be obtained using lower operatingtemperatures for the hot gases circulating through the heat transferdevice.

From the foregoing, it can be seen that the practice of this inventionresults in the production of highly oriented yarns possessing tensilestrength of an order heretofore not to be feasibly obtained. Theapparatus and process of the invention provide for the drawing of yarnsin much shorter processing distances and at high rates of speed; the 4inch length of the centrifugal heat transfer device of this invention isfound to produce results superior to those obtainable by the use of aconventional 4 foot hot slot. In addition, by using the apparatus ofthis invention, one can determine the precise temperature of the air orgas around the yarn to thereby promote better process control.

Obviously, numerous modifications and variations of the presentinvention will readily occur in the light of the above teaching. It is,therefore, to be understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed herein.

What is claimed is:

1. A process for drawing polyhexamethylene adipamide filamentscomprising the steps of drawing said filaments at a gratio greater thanabout 5.5 :1, simultaneously subjecting said filaments to the influenceof a high temperature gas vortex maintained at a temperature within therange of from about 250 to 325 C. to thereby effect high rates of heattransfer, whereby high tenacity filaments are obtained.

2. The process of claim 1 wherein said gas is nitrogen.

References Cited UNITED STATES PATENTS 10 DONALD J. ARNOLD, PrimaryExaminer HERBERT MINTZ, Assistant Examiner U.S. Cl. X.R.

3. The process of claim 1 wherein the velocity of said 15 2 71 3 734-155; 5

gas is maintained in excess of about 75 feet per second.

